Download Principles of Biology ______Lake Tahoe

Principles of Biology - Biology 102
Spring Quarter
_ Written by: Sue Kloss
Lake Tahoe Community College
Instructor: Ralph Sinibaldi
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Ch. 22 Descent with Modification
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Intro: Darwin’s Origin of Species showed unity and diversity of life was all related; had 2 main ideas: present
inhabitants of earth are descended from previous organisms, and mechanism of natural selection (NS).
A. Natural Selection - populations can change over generations if individuals that possess certain traits
leave more offspring than other individuals without those traits.
B. Adaptation 1. result of natural selection
2. accumulation of inherited characteristics that enhance an organisms ability to survive
C. Evolution - change over time in living forms, specifically, change over time of genetics of a population
1. can also mean, on large scale, gradual appearance of diversity
2. It’s the basic underpinning of science of biology that explains how change occurs over time
I. Darwin’s revolution - huge revolution socially and scientifically - shook deepest roots of science and of culture
A. Resistance to the idea of evolution - traditional beliefs - earth and all inhabitants are a few thousand yrs old
Challenged the idea that the world was created with life forms that had prevailed ever since
1. Aristotle (384 - 322 BC) viewed species as fixed
a. concluded that species could be arranged on a scale, like a ladder (scala naturae)
b. each form of life, perfect and permanent, had its rung on the ladder
c. coincides with Old Testament
d. adaptations of organisms - proof that God had designed each species w/specific purpose
2. Linnaeus -Karl Linne (1707 - 1778) Swedish physician and founder of taxonomy
a. taxonomy - naming and classifying organisms
b. binomial system of naming organisms - genus and species
c. instead of scala naturae, developed nested hierarchy - groups of species = genus, etc.
d. resemblance of species to each other indicated to Linnaeus pattern of creation
3. Cuvier - (1769 -1832) largely developed study of paleontology - study of fossils
a. fossils - remnant of earlier inhabitant of earth
b. sedimentary rocks - rock formed by sand, mud, settling over earlier layers and compressing
c. erosion may expose earlier layers
d. inferred that extinctions must have been common in history of life
e. staunchly opposed gradual evolutionary change, advocated catastrophism 1. catastrophism - flood or drought killed off organisms, area repopulated by
immigration
B. Slow change on earth - profound change can occur slowly over large time scales
1. gradulism - Hutton (1726 - 1797) - geologic features explained by gradual mechanisms still operating
a. valleys formed by rivers wearing thru rock
b. sedimentary rocks with marine fossils formed from particles carried to sea from land
2. uniformitarianism - Lyell - refined Hutton’s idea -same forces act today at same rate
a. we can measure time scales by extrapolating. eg. if sedimentary rock is laid down at an inch
per 1000 yrs, and the rock layer is 6 feet, how old is it?
3. Darwin was influenced by Lyell and Hutton, came to conclusion that earth is more than 6000 yrs old
a. estimated that forces could also act on living creatures over time producing huge change
b. several people had already argued that but did not supply mechanism for change
C. Lamarck did provide mechanism - visionary, in terms of evolution and adaptation creating fossil record, but
mechanism was wrong
a. use and disuse - body parts used frequently become enhanced - giraffes stretch necks
b. inheritance of acquired characteristics - pass modification to offspring
c. organisms have innate drive to become more complex
d. Darwin favored idea of natural selection, but believed acquired characteristics provided
variation. Modern genetics refutes this notion.
II. Origin of Species - Species change thru Natural Selection- Early in 19th century, generally believed that earth and
inhabitants was 6000 yrs old, species remained unchanged since creation
A. Darwin’s (1809 - 1882) research - loved nature as a boy, father sent him to med school. No anesthesia,
Darwin dropped out and went to ministry school. After B.A., recommended for Beagle, age 22
1. Voyage of the Beagle - survey and mapping ship
a. went all around globe, good training in science, influenced by all thinkers, esp. Lyell
b. Darwin found different fossils on different continents, found fossils on each continent more
similar to each other than to fossils in similar environments in other continents (Fig. 22.5)
c. found marine fossils in Andes, concluded that fossils had been raised there from sea
d. Galapagos - animals were like those on S. America mainland, not other islands, but existed
no where else in world.
2. Adaptations
a. finches on Galapagos - a few ancestors, many species descended (fig. 22.6)
b. Darwin was writing up his theories when Wallace beat him to the punch
c. Wallace conceded to Darwin
B. Origin of Species - 2 main ideas - evolution explains unity and diversity, and NS is mechanism
1. Descent with modification - used in lieu of term “evolution”
a. tree of life view - each fork in tree is ancestor from which all subsequent branches from that
point emerge (Fig. 22.7)
2. Natural Selection and Adaptation
a. NS broken down into 3 inferences
1. more individs than environment can sustain, only some will survive to reproduce
2. survival depends in part on inherited traits. Individuals with traits that give them high
probability of surviving and reproducing (fitness) will have more offspring
3. unequal ability of individs to survive and reproduce will cause gradual change in
population over time
b. Malthus affected Darwin - over reproduction (fig. 22.9)
c. environment shapes selection
d. artificial selection - humans modify organisms by selecting them for various traits
1. crop plants (fig. 22.10)
2. dog breeds
3. Darwin figured if humans could do it, environment could do it
e. summary of natural selection 1. differential success in reproduction resulting from interaction between individs with
various traits and their environment
2. natural selection can increase adaptation of orgs to env. (Fig. 22.11)
3. if environment changes, or individs move to new environmental, NS may give rise to
new species
III. Darwin’s theory explains a wide range of observations
A. Natural selection in action
1. Differential predation and Guppy Populations (Fig. 22.12)
2. Evolution of Drug Resistant HIV - (Fig. 22.13)
a. natural selection is an editing process, not a creating process
b. natural selection changes depending on environment
B. Homology, Biogeography, and Fossil Record
1. Homology - similarity in structure due to common ancestry - not necessarily similar function
a. Anatomical Homology (fig. 22.14)
1. homologous structures
2. vestigial organs (Fig. 22.15)
b. Molecular Homology - DNA and RNA common to all organisms - common ancestor
1. genes in common between bacteria and humans
c. Homologies and the Tree of Life )Fig. 22.16)
2. Biogeography - geographic distribution of species
a. closely related species found in same regions
b. convergent evolution can cause species of different ancestry to look similarly (Fig. 22.17)
c. endemics - native only to a certain area - many endemics on islands;
1. explains why similar islands in different parts of world have different species
3. Fossil Record - show transitional forms and record over time
a. Darwin’s theory has lasted so long because it explains so many different phenomena
C. What is Theoretical about Darwinian View of Life?
1. Theory stands up to continual tests and predictions
2. natural selection is not the only process thought to contribute to evolutionary history and the diversity
of life
Ch. 22 objectives
1. Explain the mechanism for evolutionary change proposed by Charles Darwin in On the Origin of Species.
2. Define evolution and adaptation.
3. Compare and contrast Aristotle’s scala naturae to Carolus Linnaeus’ classification scheme.
4. Describe the theories of catastrophism, gradualism, and uniformitarianism.
5. Explain the mechanism for evolutionary change proposed by Jean-Baptiste de Lamarck. Explain why modern biology has
rejected Lamarck’s theories.
6. Describe how Darwin’s observations on the voyage of the HMS Beagle led him to formulate and support his theory of
evolution.
7. Explain how the principle of gradualism and Charles Lyell’s theory of uniformitarianism influenced Darwin’s ideas about
evolution.
8. Explain what Darwin meant by “descent with modification.”
9. Explain what evidence convinced Darwin that species change over time.
10. Explain how Linnaeus’ classification scheme fit Darwin’s theory of evolution by natural selection.
11. Describe the three inferences Darwin made from his observations that led him to propose natural selection as a
mechanism for evolutionary change.
12. Explain how an essay by the Rev. Thomas Malthus influenced Charles Darwin.
13. Distinguish between artificial selection and natural selection.
14. Explain why an individual organism cannot evolve. What is the unit acted upon by natural selection?
15. Describe the experiments that supported Reznick and Endler’s hypothesis that differences in life-history traits between
guppy populations are due to selective pressure based on predation.
16. Explain how the existence of homologous and vestigial structures can be explained by Darwin’s theory of natural
selection.
17. Explain how evidence from biogeography supports the theory of evolution by natural selection.
18. Explain the problem with the statement that Darwinism is “just a theory.” Distinguish between the scientific and colloquial
use of the word theory.
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Ch. 23 - How Populations Evolve
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Individuals do not evolve, populations do.
I. Population Genetics provides foundation for studying evolution
A. Populations are units of evolution
1. population - group of individuals of same species living in same place and time, potentially
interbreeding
2. smallest unit that can evolve
3. evolution - change in heritable traits over time - eg. pesticide
4. individuals do not evolve
5. during Darwin’s time, blending hypothesis was accepted for inheritance;
a. just after Origin of Species, Mendel published his info on units of inheritance
b. Darwin never saw this paper, so had no explanation for how organisms transmit variation
in populations to offspring
B. Modern Synthesis melds population genetics with evolution, uses population genetics as a basis for
understanding evolution
1. species - group of populations of the same species that have the physical capability to
interbreed
2. population genetics is the study of how populations change genetically over time
3. Modern Synthesis- comprehensive theory of evolution that integrates idesas from many other fieldsstatistics, geneticists, biologists, biogeographers, paleontologists, etc.
4. MS is still changing to accomodate new info as it arises, eg discovery of genetic change that occurs by
other than natural selection
C. Gene Pools and Allele Frequencies
1. population - group of individuals capable of interbreeding and producing fertile offspring
2. populations may be isolated from each other or not, may have sharp boundaries or not (Fig. 23.3)
3. Microevolution is a change in a populations gene pool over time
4. gene pool = total collection of genes in a population
5. consists of alleles - alternative forms of the same gene
6. most genes have 2 or more alleles
a. if a population has only one allele at a locus of a gene, the trait is said to be fixed in the pop,
and all individuals are homozygous for that gene
7. in the body, most organisms have a gene from each parent
a. homozygous
b, heterozygous
8. a population of 500 plants with 2 alleles for flower color, Cr and Cw, has 320 red flowers, 160 pink
flowers and 20 white flowers
a. in a case where there are 2 alleles in a gene, p represents one allele, q the other.
b. p is the frequency in the gene pool of Cr, and q is the frequency of Cw.
c. in our case, p = (320 x 2) + (160 x 1) = .8
d. this means that q = .2 for a total of 1.0 (100%)
e. this is an easy example, bc. the transmission of alleles is easy to ascertain in this case. It’s not
always so easy.
9. when allele frequencies change over time, this is called microevolution
D. Hardy – Weinberg Equilibrium; allele frequencies in a pop will stay the same unless acted upon by an
outside force - so if all individuals donate gametes to the next generation randomly, and mate at random, then
the populations genes will stay the same.
1. Hardy Weinberg equation states that at a locus with 2 alleles, the 3 genotypes will appear in the
following proportions:
p2 + 2pq + q2 = 1
2. if all mating is random, it’s like shuffling a deck of cards over and over - you don’t change the proportion
of, say, Aces or Jacks.
a. shuffling, itself, can not change the frequency of one allele relative to another
3. Conditions for H-W Equilibrium:
a. Extremely large population size - the smaller the pop, the greater chance for allele fluctuations
in the next generation. Like playing roulette - if you only bet once, you generally lose
b. No gene flow - gene flow can alter gene frequencies
c. No mutations - these modify gene pool
d. random mating - preferential selection of mates alters gene pool
e. no natural selection - differential survival and reproduction of diff’t genotypes will alter allele freq.
4. In reality, HW is used not to predict the likelihood of population gene frequencies remaining the same,
but to predict likelihood of various allele changes or transmissions. book has an example for using HW to
predict freq. of disease called PKU in human population. HW also used a lot in conservation biology to try
to assess health of populations of especially endangered animals and plants.
II. Mutation and Sexual Recombination are the 2 processes that produce variation that makes evolution possible
A. Mutation - changes in nucleotide sequence of DNA - shot in the dark;
1. only mutations that produce changes in cell lines that produce gametes will be passed on
2. only a small fraction of these spread thru a population
3. point mutations- one base in a gene change can have a significant effect in a population (Fig. 23.6)
a. most probably harmless- much DNA does not code for proteins
b. organisms reflect thousands of generations of past selection, single point changes unlikely to
improve performance
c. most likely to happen when enviro is changing mutations once selected against become
favorable
4. mutations that alter gene number or sequence- mostly harmful, but if the gene duplication is neutral,
subsequent mutation or placement of the gene next to others in a chromosome may prove beneficial
(jumping genes)
a. eg gene to detect odors had one copy in remote ancestors of mammals, but gene duplication
resulted, eventually, in mammals that are able to sense many odors; humans have about
1000 olfactory genes
b. mutation rates - tend to be very low in animals and plants, avg. about 1 mutation/100,000 genes
per generation
1. in microbes with short generation spans, mutations can arise rapidly
2. HIV virus has generation span of 2 days and RNA genome, which mutates much more
rapidly than a DNA genome does. Single drugs will probably never work against HIV
c. sexual recombination- far more imp. than mutation from generation to generation in producing
variation that makes adaptation possible
1. sexual reproduction brings together fresh possibilities every generation
III. Natural Selection, Genetic Drift, and Gene Flow can Alter a Population’s Genetic Composition
A. Natural Selection - based on differential success in reproduction- those with adaptations to make them more
successful in the env. tend to produce more offspring
1. selection results in alleles being passed on in diff/t freqs than current generation
B. genetic drift - the smaller the sample, the greater the chance of deviation from predicted result (Fig. 23.7)
1. bottleneck effect (Fig. 23.8)
a. disaster in the environment reduces pop numbers - cheetahs, elephant seals
b. elephant seals hunted almost to extinction, 20 individs known
c. protected, then pop rebounded to 30000,
d. at 24 loci, NO g.v.
2. . founder effect - when a few individs become isolated from larger pop
3. migration, or gene flow - reduces differences btn pops, introduces new genes
IV. Natural Selection is the primary mechanism of adaptive evolution
A. Genetic Variation - variations that are heritable are the raw material for natural selection
1. only some is heritable - when and why? (phenotype vs. genotype)
2. some is developmentally related (Fig. 23.9)
B. Variation within a population
1. genetic polymorphisms - if 2 or more “readily noticeable” forms exist in pop
a. human height is not polymorphic, it is continuous - lots of genes control it.
b. polymorphisms contribute to variation
2. measuring genetic variation - determine the amt. of heterozygosity in a pop. eg. elephant seals don’t
have a high amt. of heterozygosity.
C. Variation between populations - geographic variation exists in most species
1. diff. in gene pool btn difft populations
2. cline - graded change in a trait along a geographic axis
D. Adaptive changes result when natural selection favors certain designs
1. individuals are all varied in a population
a. Some individuals leave more offspring than others
b. If environment changes, successful individuals will probably change
2. evolutionary fitness
a. fitness - contribution to the gene pool relative to other individuals
b. relative fitness- contribution of a genotype to next generation - eg. sickle cell anemia in Africa is
enhancing relative fitness of that genotype
c. alleles that are neutral or negative may be perpetuated if an individuals overall fitness is high
d. survival AND fertility are both important in fitness
E. Three general outcomes of natural selection (fig. 23.12)
1. stabilizing selection
2. directional selection
3. diversifying selection
F. Sexual Selection - natural selection for mating success
1. can result in sexual dimorphism (Fig. 23.15)
a. intrasexual selection - competition within a gender produces dimorphism- mountain goats with
big horns that fight over females; female lemurs compete
b. intersexual selection - one gender chooses the other, most often, females choose males
1. Darwin - confused bc many traits (peacock feathers) do not enhance survival
showy animals tend to be healthy
2. Evolutionay enigma of sexual reproduction
a. sex is “expensive” - only half your genes go on in each offspring
b. but gv is worth the loss, consider resistance to disease.
G. Why can’t Natural Selection Fashion perfect organisms?
1. evolution is limited by historical constraints - editing process, not a creative one - human backs
2. Adaptations often compromises- our hands, wrists and opposable thumbs give us lots of advantages,
and also lots of sprains and injuries
3. chance and natural selection interact - the best basketball players are not playing in the NBA
4. selection can only edit existing variations - only the fittest phenotypes currently among us can be
selected for, new alleles do not arise on demand
Ch. 23 Objectives
1. Explain the statement “It is the population, not the individual, that evolves.”
2. Explain how Mendel’s particulate hypothesis of inheritance provided much-needed support for Darwin’s theory of evolution
by natural selection.
3. Distinguish between discrete and quantitative traits. Explain how Mendel’s laws of inheritance apply to quantitative traits.
4. Explain what is meant by “the modern synthesis.”
5. Define the terms population, species, and gene pool.
6. Explain why meiosis and random fertilization alone will not alter the frequency of alleles or genotypes in a population.
7. List the five conditions that must be met for a population to remain in Hardy-Weinberg equilibrium.
8. Write the Hardy-Weinberg equation. Use the equation to calculate allele frequencies when the frequency of homozygous
recessive individuals in a population is 25%.
9. Explain why the majority of point mutations are harmless.
10. Explain why mutation has little quantitative effect on allele frequencies in a large population.
11. Describe the significance of transposons in the generation of genetic variability.
12. Explain how sexual recombination generates genetic variability.
13. Explain the following statement: “Only natural selection leads to the adaptation of organisms to their environment.”
14. Explain the role of population size in genetic drift.
15. Distinguish between the bottleneck effect and the founder effect.
16. Describe how gene flow can act to reduce genetic differences between adjacent populations.
17. Define average heterozygosity
18. Define a cline.
19. Define relative fitness.
a. Explain why relative fitness is zero for a healthy, long-lived, sterile organism.
b. Explain why relative fitness could be high for a short-lived organism.
20. Distinguish among directional, disruptive, and stabilizing selection. Give an example of each mode of selection.
21. Explain how diploidy can protect a rare recessive allele from elimination by natural selection.
23. Describe how heterozygote advantage and frequency-dependent selection promote balanced polymorphism.
24. Define neutral variations. Explain why natural selection does not act on these alleles. 25. Distinguish between intrasexual
selection and intersexual selection.
26. Explain how female preferences for showy male traits may benefit the female.
27. Describe the disadvantages of sexual reproduction.
28. Explain how the genetic variation promoted by sex may be advantageous to individuals on a generational time scale.
29. List four reasons why natural selection cannot produce perfect organisms.